<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>Title</title>
  <style>
    body{margin: 0;}
    .box{display: flex;width: 1000px;height: 350px;margin: 0 auto;}
    .child{flex: 1;}
  </style>
</head>
<body>
<div class="body"></div>
<div class="box">
  <div class="child" style="background-color: aqua;">1</div>
  <div class="child" style="background-color: purple;">2</div>
  <div class="child" style="background-color: seagreen;">3</div>
</div>
<div class="box">
  <div class="child" style="background-color: greenyellow;">4</div>
  <div class="child" style="background-color: mediumblue;">5</div>
</div>
</body>
</html>